Glass Formation and Properties in the System Calcia-Gallia-Silica

The glass-formation region of the calcia-gallia-silica system was determined. The glasses within this region were measured to have a density of 3 to 4 g/cm³, a refractive index of 1.6 to 1.73, an Abbe number between 35 and 58, a thermal expansion coefficient of 6.5 × 10⁻⁷/°C to 11.5 × 10⁻⁷/°C, softening temperatures between 730° and 790°C, and a Vickers microhardness of 5.2 to 7.3 GPa. Crystalline phases were identified along the glass-formation boundary. Infrared transmission spectra were used to explain glass structures and their effect on glass properties. The results suggest that the role of calcia in the glass structure is similar to that for calcia in calcium aluminosilicate glasses.     

Color and Selected Properties of PbO─BiO1.5─GaO1.5 Glasses

The density; molar volume; thermal expansion coefficient; dissolution rate in water, HC1, and NaOH; glass transition and crystallization temperatures; and the absorption edge in the ultraviolet-visible and infrared were measured for PbO─BiO1.5─GaO1.5 glasses. The range of compositions investigated was x PbO (100 − (x + y) )BiO_1.5. yGaO_1.5 for x between 20 and 60 cat% and y of 20, 25, 30, and 35 cat%. The glass-forming tendency increased with increased GaO_1.5 and decreased with increased PbO or BiO_1.5. The compositional dependence of these properties was consistent with the weight, size, charge, and bond strength of the cations. The Ga^{3 +} ions in these glasses are believed to act primarily as network-forming cations, whereas the majority of the Bi³⁺ and Pb²⁺ ions behave as network-modifying cations. It is suggested that a small friction of the lead ions are present as Pb⁴⁺. Depending upon melting conditions, these glasses ranged in color from brown to yellow. Various attempts, including containerless melting, were made to obtain colorless glasses, but no conditions were found which totally eliminated the color. The least color (pale yellow) was obtained when the glasses were melted in an air or nitrogen atmosphere in an alumina or gold crucible.     

Modelling of addition polymerization processes — Free radical,ionic, group transfer,and ziegler–natta kinetics

A brief review of addition polymerization processes is presented with a summary of the key characteristics classified by kinetic mechanism (free-radical, anionic, cationic, group transfer, or Ziegler–Natta), phase behavior, and reactor type. A practical approach to modelling in the industrial R & D environment is discussed in terms of a CAD package for polymerization processes.     

A microscopic model for catalytic surfaces—I. Catalytic wires and gauzes

A new “fuzzy wire” model of catalytic wires and gauzes is presented which is in good agreement with observed ignition, extinction, and flickering phenomena. The model predicts both simple harmonic oscillations as well as a wide variety of nonperiodic chaotic oscillations. Quantitative comparisons with data for butane oxidation and cyclohexene oxidation are quite good; however, the very long period oscillations observed for H₂ and CO oxidation are not predicted by the simplest forms of the model.     

Mounting media for the microscopical examination of rubber-reinforced polymers

Mounting media for examining rubber reinforced copolymers using the phase microscope are described. The mounting media are based on cinnamaldehyde as the basic solvent with suitable adjustments made depending upon the copolymer under examination.     

On the steady state and dynamic behaviour of permeable,isothermal catalysts

In this paper we suggest a lumping procedure for distributed reacting systems which has the property of uniform convergence to the exact solution. We apply this procedure to the analysis of permeable isothermal catalysts and treat in detail the case of Langmuir-Hinshelwood rate expressions. As a special example, we analyse the hydrogenation of ethylene over platinum/alumina and show that multiple steady states are predicted for isothermal catalyst pellets for certain values of the external partial pressures and Thiele Modulus.     

AN APPARATUS FOR THE DETERMINATION OF ADSORBED AIR1

Some possible ceramic applications of the Toepler mercury pump as employed in determination of gases in various materials are discussed. The procedure followed in measuring the gases given off by a clay slip at reduced pressures is described. It was found that 4.65% of gases by volume are removed from a sample of clay slip by reducing the pressure on the sample to boiling (25 mm.). An additional 0.18% of gases was cvolved between the boiling pressure and 1.8 mm. at which pressure the sample was dry.     

Partial removal of hafnium from zirconium through the reactions of tetrachloride vapours with solid sodium chloride

A pyrometallurgical method for partial separation of hafnium from zirconium has been investigated. The method involves continuous reaction between a flowing gas mixture of zirconium tetrachloride and hafnium tetrachloride with solid sodium chloride in a packed bed reactor. The solid-vapour reaction enriches the vapour phase with respect to zirconium tetrachloride. This may be attributed to a more favourable reaction for hafnium tetrachloride. The influence of a number of parameters, e.g. temperature, gas flow rate, particle size and bed length, has been studied. Decreases in flow rate and particle size and increase in bed length are found to favour separation, while temperature has little effect. A simple equation has been derived to explain the experimental observations.